Kyocera KC130 output issue...diodes?

Comments

Gosh, my new solar system uses six Kyocera KD210GX-LPU panels. I hope this isn't a Kyocera-wide problem with all of their panels. Some of mine get shaded in the winter months. Are there reports of others having similar problems with Kyocera panels? Should I be concerned?

i wouldn't get alarmed, but it's something you should be aware of. it would be a good idea to check on your pvs several times a year to see if any may be showing the signs of a failure. do know that this could happen on other pv manufacturers with similar designs as well so it isn't necessarily confined to kyocera.

I heard back from Kyocera.
They are sending me enough diodes to completely replace all the diodes in the two subject panels (12 diodes)
I asked for an equvalent part number to the R3CM diode...This is what they gave for a part number: MUR 4100E
I found this at Mouser and Digikey. The specs are just slightly different, but they look like they will work fine.
I'm going to order some to have on hand just in case for future issues if they arise.

I heard back from Kyocera.
They are sending me enough diodes to completely replace all the diodes in the two subject panels (12 diodes)
I asked for an equvalent part number to the R3CM diode...This is what they gave for a part number: MUR 4100E
I found this at Mouser and Digikey. The specs are just slightly different, but they look like they will work fine.
I'm going to order some to have on hand just in case for future issues if they arise.

I would say that a MUR4100E would be a very poor choice for replacements. At 4 amps the Vf is 1.85 vdc. That is 7.4 watts. Will likely crack their casing. At 100 deg C they are derated to 2.9 amps.

If you must stick with axial leads diode go with MUR550APF. Another option is MUR460. TO-220 cases are much better and you have a lot more selection options. A 10 amp, 600v or higher breakdown voltage would be pretty solid. Even if your panel stack is greater then 500 vdc it is very very unlikely that any bypass diode would see over 50 vdc reverse bias during operation. You would have to have massive multiple failures for a bypass diode to see the stack voltage.

I think the T-220 case would be difficult to mount in the junction box. The axial lead diodes mount to what I would call somewhat of a heatsink as the metal pads and hold down pads are rather good sized in comparison to the diodes. I'm wondering why Kyocera would recommend a substandard diode to me. ???

It may be just a case of engineering philosophy. Bypass diodes are like a skydiver's reserve parachute. Most of the time it may never be used but when you need it, it better work.

If bypass diodes come into play, most of the time it is in the morning where easterly trees give partial shading or evening with trees to the west. Illumination levels in morning or afternoon are relatively low so maybe a couple amps maximum have to be bypassed. Worse case is clear sky at high noon when a leaf or large bird splatt hits over a single cell. The bypass diode has to take full panel current capability. Although less probable then a morning or afternoon tree shading it is not an impossible situation. Do you want the risk the possiblity of destroying a cell that scraps the whole panel?

I certainly wouldn't want to risk losing a panel to one cell, but I also don't want to risk Kyocera not warranting a panel because I used a different diode than they use/recommend. I guess that still brings me back to the point of just ordering the original diode.

i think that would be pretty pi**y of them to reject the use of better diodes after recommending ones that aren't as good. i believe they are using 3 parallel diodes per bypass and i see nothing wrong in going to better diodes even to the degree you may be able to use less numbers of diodes if they are rated for better current handling.

I completely agree Neil, but I also have got burned more than once by manufacturers (and stores) looking for any way to avoid a claim. Kyocera has been very good to me regarding the KC120 issue in the past, but there is always a first time.

That would be just plain bad engineering. First, 36 cells is too many for one bypassing. Second, putting diodes in parallel is about the same as putting fuses in parallel. Putting a 1 ohm ten watt resistor in series with each of the three diodes for current balancing would help, but you would have room for a TO-220 diode if you could do that.

If the "paralleled" diodes are on separate solar cell/panel strings, then current sharing is not an issue. Solar cells are (more or less) current sources so they "natural share current" based on their capabilities, not on the general resistance variations in the wiring.

thanks for the correction, i've never totally followed the cell paths to see how they are bypassed...i was just guessing because the voltage dropped in half when one of the two sets of 3 diodes had failed

If you have two sets of three diodes in parallel the panel is bypassed in two groups of 18 series cells. Two groups of 18 cells would be a normal configuration for a 36 series cells panel. It is stupid to put three diodes in parallel as one of the three will take most of the current. If that is what Kyocera is doing, then shame on them. When it fails (if fails open instead of shorted) another one of the two remaining parallel diode takes most of the current, then it fails and so on to the last one. (unless each diode is capable of supporting the total current, in which case you only need one diode). Since you said you have a drop in panel output voltage then one of the diodes failed shorted, end of story.

As I said earlier, three diodes in parallel is effectively one active diode and two providing some additional heat sinking due to their physical presence. To put three diodes in parallel they have to be exactly matched and thermally tied together. This basically means they are on the same semiconductor die. Three separate diodes of same part numbers will not assure matching. Thermally strapping the packages together is not sufficient as there is some thermal resistance from the die to mounting leads and package. The diode die carrying the most current will get hotter driving an increase in the mismatch with the other diodes.

seeing room as a problem for replacing the 3 diodes with a single diode, maybe you can use 2 6a diodes instead. some sharing will still occur, but being of higher current ratings to begin with they may be less likely to blow.http://www.radioshack.com/product/index.jsp?productId=2062591
i don't know if the larger barrel size will be a problem in the allotted space or not as the barrel is likely to be longer, but not by much. fatter shouldn't matter much as you would be putting in 2 instead of 3. of course you can still go with kyocera's idea of 3 smaller diodes

I just received the replacement diodes from Kyocera....They sent me the MUR4100E diodes.
I don't know if that means this is the diode they are currently using in their panels. Maybe someone here has some current model Kyocera panels which they can check.

After reading some of the responses here, I'm inclined not to use them and install the MUR550APF diodes instead.

james,
imo, if you have some of the 550apf diodes then use them as they show better vf characteristics and will reduce losses by 3-4w per bypass over the 4100e diodes they sent you. maybe try both and compare as it will show up in the voc under relatively similar conditions making comparing them fairly easy. if you do compare them then let us know what you find.

Bypass diodes have no effect of VOC, unless they go bad. They do have a very small amount of leakage current but this should be very small compared to any illumination current, or leakage within the cells themselves.

MUR550APF is out of production so you may have problems finding them. Again, a 500 to 600 volt breakdown diode that can handle 5 amps in the high heat of the panel environment is good. It doesn't have to be a fast recovery diode. The lower the forward voltage drop at 5 amps the better as it will generate less internal heating. Check for their temp derating. Many spec less current capability at higher ambient temps. 4 to 5 watts of heat generation by a leaded diode will burn your fingers if you touch the diode. Heat generation is Vf times forward current.

I still think you could substitute one TO-220 packaged diode in the same space taken by three parallel leaded diodes.

oops, you're right rc as these parallel the cells and are not in series with them so he can forget the voc measurements. thanks for the correction. see what happens when you aren't fully awake yet. the lower vf from the 550apf diodes would lessen the losses by at least a couple watts when that part is shaded causing the bypass diodes to engage though.

James, if you're still out there... I want to thank you for all the research you did and especially the comments on this forum. I was just given a couple used Kyocera KC130's that both had all the diodes blown out when the person that gave them to me was "tinkering". After reading your comments, I felt confident ordering the MUR550APF as well.

For anyone else that's still looking for help finding the parts:

1) If you want to go with Kyocera's suggestion: Search eBay for: "MUR4100" (many available from china for cheap)